In the past, numerous different methods have been used for singulating or dicing a semiconductor wafer, the process of dividing a semiconductor wafer into individual devices. The two most widely used methods at this time are sawing using a diamond saw blade and laser scribing using a focused laser beam to cut through the wafer. Neither method is ideal. Both result in a significant loss of material during the cutting process. As the size of semiconductor devices get smaller, the width of the line of lost material during the dicing process becomes comparable to the width of the device. If the width of the line of material lost during the scribing process could be made significantly smaller, many more devices could be made on each wafer, resulting in a large savings in the cost of fabricating the devices. In addition, both the sawing and laser scribing cause damage along the cut edges of the devices that can result in rejected devices during visual inspection and in some cases cracking that can cause device failure in the field.
Since the invention of plasma and reactive ion etching in the 1970s, many individuals have proposed using these processes for wafer singulation. These processes potentially could decrease the material loss during the dicing process by etching very narrow scribe lines through the semiconductor wafer. In addition, since the etch process takes place at a microscopic level and involves no heat or mechanical grinding, the edge of the semiconductor devices are not damaged by the process. In order for a plasma etching or a reactive on etching process to be effective in wafer dicing, it would have to etch very deep, narrow trenches in the scribe streets of the semiconductor wafer and it would have to etch at a very fast etch rate to be economically attractive. These two conditions have been achieved by Teixeira, et al (U.S. Pat. No. 6,417,013) building on the work of Laemer, et al., (U.S. Pat. No. 5,501,893). The single issue remaining to be resolved was a cost effective method of removing the back metal that remains in the scribe street after the etch process is completed. My U.S. Pat. Nos. 8,445,361 and 8,450,188 address this matter.
Semiconductor wafers usually have one or more metal layers applied to the back of the wafer during fabrication to provide ohmic contact and/or ease of die attach during packaging of the devices. These layers of metal are not readily etched using dry etch processes.
U.S. Pat. No. 8,445,361, issued May 21, 2013, relates to a method of dividing a semiconductor wafer having a metal layer including removing all or substantially all of the semiconductor material in scribe streets while the wafer is supported by a support, turning over the wafer and while using a second support to support the wafer, introducing a heat energy flux into the metal layer to remove metal of the metal layer from the scribe streets.
U.S. Pat. No. 8,450,188, issued May 28, 2013, relates to a method of dividing a semiconductor wafer having a metal layer and a semiconductor material layer including the step of cutting the semiconductor material layer along scribe streets without cutting the metal layer, turning over the wafer, and cutting the metal layer along the scribe streets.
U.S. Pat. No. 8,664,089 (Burghout et al.), issued Mar. 4, 2014, discloses a semiconductor die singulation method wherein semiconductor die are singulated from a semiconductor wafer having a back metal layer by placing the semiconductor wafer onto a carrier tape with the back metal layer adjacent the carrier tape, forming singulation lines through the semiconductor wafer to expose the back metal layer within the singulation lines, and fluid machining the semiconductor wafer to remove the back metal layer from the singulation lines.
Burghout et al. describes a method of removing the back metal layer by flipping the wafer over on another piece of adhesive plastic film after the plasma etch has been completed to expose the back metal to a fluid ejected from a nozzle. While Burghout et al. employs the term “pressurized fluid” when relating to the process for removing the back metal, in the Burghout et al. approach the fluid is pressurized only in order to eject it through a nozzle. However, after the fluid leaves the nozzle, under a basic law of physics, the fluid must be at atmospheric pressure and is no longer a “pressurized fluid”. It is not a “pressurized fluid” when it impinges on the metal layer to affect its removal. The Burghout et al. removal process is being carried out by the momentum of a previously pressurized fluid.